Jonah Hill, world’s worst babysitter. Must have sounded like such movie magic that the makers of “The Sitter” grabbed the first three brats they found on the street, shoved them in a minivan with Hill and started filming.

As broad, dumb comedy goes, it’s not a bad idea to cast Hill as a chubby slacker roped into a hellish night tending to a high-maintenance brood. Yet other than Hill’s admirable work ethic trying to squeeze laughs out of this dismally underdeveloped scenario, “The Sitter” has nothing going for it.

Not even its fleeting length. Take away the opening and closing credits, and you’re left with not much more than an hour of actual movie. But it feels much, much longer, watching “The Sitter” slog along from one rotten gag to the next.

The movie’s also a serious racial offender, parading a gang of black actors around as hoods stealing cars, talking jive or looking for a fight.

Director David Gordon Green — who started as an indie-film prodigy with such small, smart dramas as “George Washington” and “All the Real Girls” before going Hollywood with the 2008 hit “Pineapple Express” — delivers his second bad, raunchy comedy of the year, after last spring’s “Your Highness.”

He’s single-handedly jeopardizing the goodwill R-rated comedy has gained in Hollywood from such dirtier-minded hits as “Bridesmaids,” ‘’Bad Teacher” and others in the Judd Apatow mold.

Apatow protege Hill, who leaped from a bit part in “The 40-Year-Old Virgin” to stardom in “Superbad,” plays Noah Griffith, an idler kicked out of college, living with his divorced mom and whiling away his time watching TV. His mother guilts him into taking a babysitting job for family friends, and from there, the merry mayhem is supposed to take off.

It’s all just muck from then on, except for an occasional throwaway line that’s worth a chuckle. Screenwriters Brian Gatewood and Alessandro Tanaka’s verbal jokes are mostly mindless, though, and “The Sitter” really fails in the physical comedy department with an assault of mean, humorless sight gags.

The filmmakers try to sneak in tender, nurturing moments with each of the three kids: 13-year-old social outcast Slater (Max Records of “Where the Wild Things Are”); little sister Blithe (Landry Bender), a junior party girl whose painted-[filtered word] makeup is not hilarious, as the filmmakers apparently believed, but simply creepy; and their adopted Hispanic brother, Rodrigo (Kevin Hernandez), a destructive monster with an arsenal of cherry bombs.

Bender is shrilly annoying, Hernandez is obnoxiously annoying, while Records is merely annoying. The same goes for Ari Graynor as Noah’s sort-of girlfriend, whose promise of sex sends him out cruising Manhattan in search of cocaine, taking the kids along in their parents’ minivan. (How did tubby loser Noah hook up with a hottie like Graynor? Who really cares?).

“The Sitter” bumbles along in an awkward collection of episodes as Noah encounters obstacle after witless obstacle, weirdo after dreary weirdo. Saddest among his new acquaintances is Sam Rockwell as a psychotic drug dealer. Rockwell is pals with Green, putting in a fine performance in the director’s 2007 drama “Snow Angels.” Friends deserve better than what Rockwell gets in “The Sitter.”

Hill is no funnier here than his co-stars, yet he’s clearly trying to make “The Sitter” work. His earnestness almost makes you believe in Noah, if not in the mess of miserable action swirling around him.

Advice to parents, and everyone else, looking for some decent entertainment to babysit your eyeballs for a while: don’t hire “The Sitter.”

“The Sitter,” a 20th Century Fox release, is rated R for crude and sexual humor, pervasive language, drug material and some violence. Running time: 81 minutes. One and a half stars out of four.